Drive decay theory of self-stimulation: Refractory periods and axon diameters in hypothalamic reward loci

I. Szabó, L. Lénárd, B. Kosaras

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In seven rats with low-threshold self-stimulation loci the diameter of the lateral hypothalamic myelinated axons were measured by light and electron microscopy (Experiment 1). In addition, the electron microscopic study of the axon diameters was continued in 8 loci after an experiment of confirming earlier demonstration of the 0.5 to 0.6 msec long absolute refractory period of the hypothalamic reward system (Experiment 2). Most axon diameters ranged between 0.6 to 1.3 micra. 96.5 and 98.4 per cent of the examined 3251 axons had diameters less than 2 and 3 micra, respectively. In 5 self-stimulation loci we did not observe any axons ranging between 3 to 6 micra in diameter. Measurements of both the axon diameters and the refractory times in the fornix and anterior commissure (Experiment 3) suggest that the absolute refractory period of 0.8 to 1.1 msec measured by Deutsch [5] can only belong to the axons in the lateral hypothalamic self-stimulation loci, but the other period of 0.5 to 0.6 msec would require myelinated axons of about 5 to 6 micra in diameter. Consequently, the findings support the view that the improvement of excitability occurring after the end of a post-stimulatory delay period of 0.5 to 0.6 msec is due to the onset of synaptic activation instead of recovery from axonal refractory state.

Original languageEnglish
Pages (from-to)329-343
Number of pages15
JournalPhysiology and Behavior
Issue number3
Publication statusPublished - Mar 1974



  • Anatomy of reward
  • Anterior commissure
  • Axon diameters
  • Drive decay theory
  • Fornix
  • Lateral hypothalamus
  • Refractory periods
  • Self-stimulation

ASJC Scopus subject areas

  • Experimental and Cognitive Psychology
  • Behavioral Neuroscience

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